For many years I have used a product called SyncBack. In addition to more traditional backups, it can mirror (copy changes from A to B) or synchronize (copy changes from A to B and from B to A). You can set it to run on a schedule or manually.

They have three versions available, SyncBackFree, which should be adequate for your needs, and two paid versions, SyncBackSE and SyncBackPro which add features like backing up to DVD, Google Drive or FTP.

If you're comfortable with the command line and can install tools with MacPorts or homebrew, I'd recommend rsync. (Versions exist for windows using the cygwin tools, and linux, of course).

Then sync things from your local maching to the remote, and vice-versa

rsync --archive --update mydir remote:mydir

rsync --archive --update remote:mydir mydir

You can put these into the mac/unix scheduler, crontab, and run them every few hours. It's extremely efficient at transferring once you've established a copy. I use it to keep 2 TB synced from home over my internet connection to an offsite backup at work.

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